In an article published in PNAS, researchers have used the recombinant expression of more than 2000 Human Secretome Project proteins to investigate the factors influencing recombinant protein expression in CHO cells.

Protein secretion is a fundamental biological process essential for cellular function, and the secreted proteins are important in mediating cellular interactions with the extracellular environment and regulating biological processes such as cellular homeostasis and cell signaling. Understanding which factors that can affect protein secretion is not only important to better understand disease, but also to get insights in how to optimize yields and protein quality in host cells to advance the production of recombinant proteins and biotherapeutics.

In this study the recombinant expression of more than 2000 secreted proteins in Chinese Hamster Ovary(CHO) cells was used to investigate factors leading to the large variability in total protein expression and to only about 60% of the proteins being expressed above the quality threshold. Statistical and ML methods were used to quantify how 218 protein features affected the expression and secretion of proteins in CHO.

In total these features accounted for about 15% of the variability in recombinant protein expression, and the results show that MW, the presence of disulfide bonds, cysteine composition, and N-linked glycosylation had the strongest effect. Further, it was shown that successful producers upregulate UPR and folding machinery, whereas failed producers upregulate ERAD/ERpQC (ER protein quality control). Another important finding was that the variation in recombinant protein expression could not, as previously suggested, be explained by transgene mRNA abundance which only explained less than 1% of the variation in protein titer.

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